The petrogenesis of leucogranitic dykes intruding the northern Semail ophiolite, United Arab Emirates: field relationships, geochemistry and Sr/Nd isotope systematics

The Khawr Fakkan block of the Semail ophiolite (United Arab Emirates) exhib its a suite of 10-100 m scale metaluminous to peraluminous granitic intrusi ons, ranging from cordierite-andalusite-biotite monzogranites to garnet-tou rmaline leucogranites, which intrude mantle sequence harzburgites and lower crustal sequence cumulate gabbros. Structural constraints suggest that the subduction of continental sedimentary material beneath the hot proto-ophio lite in an intra-oceanic arc environment led to granulite facies metamorphi sm at the subduction front and the generation of granitic melts which were emplaced up to the level of the ophiolite Moho. Compositions indicate the a nalysed granitoids were largely minimum melts that crystallised at variable a(H2O) and pressures of 3 to 5 kbar. The LILE (Sr, Rb and Ba) covariation modelling suggests that the granitoids formed largely by the dehydration me lting of muscovite rich metasediments. Initial Sr-87/Sr-86 ratios Of analys ed dykes vary between 0.710 and 0.706 at initial epsilon(Nd) values of betw een -6.3 and -0.5. Cogenetic units of a composite sill from Ra's Dadnah yie ld a Sm-Nd isochron age of 98.8 +/- 9.5 Ma (MSWD = 1.18). Geochemical and i sotopic characteristics of the analysed granitic intrusions indicate that t he subducted continental material was derived from oceanic trench fill (Hay bi complex) sediments, preserved as greenschist (Asimah area) to granulite facies (Bani Hamid area) ophiolitic metamorphic sole terranes. The Sr Nd is otope systematics suggest that hybrid granitic melts were derived from pre- magmatic mixing of two contrasting subduction zone sources.